Classifications
Anthracite is classified into three grades, depending on its carbon content. Standard grade is used as a domestic fuel and in industrial power-generation. The rarer higher grades of anthracite are purer – i.e., they have a higher carbon content – and are used in steel-making and other segments of the metallurgical industries. Technical characteristics of the various grades of anthracite are as follows:
| Standard grade anthracite | HG anthracite | UHG anthracite | Coke | |
|---|---|---|---|---|
| Moisture (maximum) | 15% | 15% | 13% | 5% |
| Ash (maximum) | 20% | 15% | 12% | 14% |
| Volatiles (maximum) | 10% | 10% | 5% | 2% |
| Fixed carbon (minimum) | 73% | 80% | 85% | 84% |
| Sulphur (maximum) | 1% | 1% | 0.6% | 0.8% |
| Phosphorus | 0.02% | 0.002% | 0.002% | 0.04% |
Anthracite is divided by size mainly into applications that need lumps (typically larger than 10mm) - various industrial processes where it replaces metallurgical coke, and domestic fuel - and those that need fines (less than 10mm), such as sintering and pelletising.
The common American classification by size is as follows:
Lump, steamboat, egg and stove coals, the latter in two or three sizes, all three being above 1½ in (38 mm) size on round-hole screens.
| Classification | Minimum Size (inches) | Maximum Size (inches) |
|---|---|---|
| Chestnut | 7/8 | 1½ |
| Pea | 9/16 | 7/8 |
| Buckwheat | 3/8 | 9/16 |
| Rice | 3/16 | 3/8 |
| Barley | 3/32 | 3/16 |
The primary sizes used in the United States for domestic heating are Chestnut, Pea, Buckwheat and Rice, with Chestnut and Rice being the most popular. Chestnut and Pea are used in hand fired furnaces while the smaller Rice and Buckwheat are used in automatic stoker furnaces. Rice is currently the most sought after size due to the ease of use and popularity of that type of furnace.
In South Wales a less elaborate classification is adopted, but great care is exercised in hand-picking and cleaning the coal from particles of pyrites in the higher qualities known as best malting coals, which are used for kiln-drying malt.
Anthracite dust can be made into briquettes and is sold in the United Kingdom under trade names such as Phurnacite, Ancit and Taybrite.
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